Power is an instantaneous value; the wind turbine produces so many Watts (or kilowatts) of power at a specific time depending on existing conditions. Power output will change continuously throughout the day. Energy includes a time factor and is measured in Watt-hours or kilowatt-hours (kwH). This is what the wind turbine owner is interested in – energy production from the wind turbine over a period of time; a day, month or year.